Biological waste treatment is a process which uses microorganisms to consume dissolved organic contaminants in waste water and convert them to additional microorganisms. In aerobic systems, microorganisms are mixed with waste water containing organics and aerated with oxygen for a predetermined period of time. After aeration, the mixture of microorganisms and water is transferred to a settling zone or clarifier tank where the solid organic contaminants and microorganisms settle, allowing the water at the upper portion of the clarifier tank to be removed while leaving organics in the clarifier.
The settled organic matter lies on the bottom of the tank and must be removed periodically to prevent excessive buildup of microorganisms and sludge at the bottom of the tank. The removal is usually accomplished by scraping it off the bottom of the tank.
Control of the sludge at the bottom of the tank is very critical in adjustment of the sewage treatment plant. In order to maintain the proper amount of microorganisms in the aeration tank, the proper amount of sludge must be returned to the aeration zone from the clarifier zone, thus maintaining the microorganisms at the proper level.
Aerobic waste treatment for organic carbon removal utilizes biological actions similar to those found in natural waterways. Treatment plants are designed to speed up natural water purification processes and provides means for treating and disposing of waste products from water. "Sludge" is made up of mixed culture of bacteria called Zoogloea ramigera. Other microorganisms such as paramecia are also present and are referred to as free swimmers. All these organisms remove some inorganics, by using the materials for food and as essential nutrients.
Microorganisms remove waste water contaminants by absorption and adsorption. Adsorption involves adhering contaminants to the surface of the cells. Material entrapped in this manner is carried by the cell until it is completely digested or disposed of as waste sludge. Absorption involves taking contaminants into the cell. Materials absorbed are completely digested by the microorganisms. In both cases the end products of the process are CO.sub.2 and H.sub.2 0. Sludge containing substances are not readily degradable can eventually metabolize these substances in the digester or holding tank. Digested sludge is relatively inert and can be readily dewatered for landfill.
Sludge settling and compaction characteristics are a primary requisite to successful operation of an activated sludge process. With poor settling sludge, solids carried over the effluent will not only increase TSS (Total Suspended Solids) but also increase BOD (Biological Oxygen Demand) which results in loss of process performance. Poor compaction results in a low return sludge concentration and will limit the MLSS (Mixed Liquor Suspended Solids) concentration in the aeration zones.
Metabolism and energy levels of the biology play an important role in whether or not the cells will coagulate and form large floc particles for good settling characteristics. Performance is based on having enough biological sludge to readily consume the organic pollutants present in the waste water. If biological sludge is in excess, some of it will die and the residue will be discharged in the effluent as part of the TSS.
Failure to remove the sludge periodically will result in an anaerobic condition which will sap the oxygen from the effulent and result in a low DO (Dissolved Oxygen) contact and have adverse results in the receiving stream of water. The anaerobic sludge will eventually float to the top of the settling tank and be carried over into the effluent stream itself. In addition, the contaminated sludge will result in equipment breakdown in the sewage treatment plant.
Heretofore, scrapers which were rigid enough to scrape the sludge from the bottom of the tank without passing or sliding over the sludge required heavy rigid structures to support the scraper blade. This structure must necessarily be submerged in the liquid of the clarifier tank. Two problems are developed from using this type of structure: (1) the structure is subject to the highly corrosive liquid of the clarifier tank and is usually oxidized by passage through the clarifier, thus weakening the structure until it collapses (2) the structure creates eddy currents within the liquid itself by liquid passing therethrough, which tend to keep the organic material and settled sludge suspended in the liquid, which defeats the purpose of the clarifier tank.
My invention is directed at providing a more efficient scraper to remove the sludge.